A structural transect through the High and Middle Atlas of Morocco

The surface and crustal structure of the Atlas ranges of Morocco are described by a structural section from the Foreland basin of the Rif to the Sahara craton. The Atlas ranges derive from inversion of Jurassic extensional or transtensional troughs during the Cenozoic, and they consist of dominantly thick-skinned thrusts and folds separated by tabular plateaux. Paleozoic basement is downwarped in synclinal areas up to 3 kin below sea level, but is exposed at the surface in the peripheral plains, thus lying at a higher regional elevation than in much of the interior of the ranges. Synorogenic basins are poorly preserved. Based on the surface geology and available geophysical data, a reinterpretation of the crustal structure is proposed, in which the thrust system of the High Atlas is interpreted to cut into the lower crust and offset the Moho. The moderate amount of shortening along the transect (about 12%) contrasts with the elevated Atlas topography, which cannot be explained by crustal thickening alone. The presence of Cenozoic alkaline volcanics, widespread in the Middle Atlas, together with low seismic velocities suggest the existence of a thermally anomalous mantle contributing to uplift in the region. (C) 2004 Elsevier Ltd. All rights reserved.